1. Field of the Invention
The present invention relates to a mobile electric flash-butt welding unit for welding together adjacent ends of track rail sections extending in a longitudinal direction, each track rail section having a gage side and a field side, and the welding unit comprising a pair of welding heads displaceable in the longitudinal direction towards each other, each welding head comprising two tong-like parts pivotal towards each other and carrying clamping electrodes for engaging the sides of a respective one of the rail section ends, and actuating cylinder means extending in the longitudinal direction and connected to each welding head for pressing the welding heads in the longitudinal direction towards each other.
2. Description of the Prior Art
U.S. Pat. No. 4,929,816, dated May 29, 1990, discloses such an electric flash-butt welding unit vertically adjustably mounted on a mobile machine running on the track. The pivotal clamping and welding tongs are pressed by hydraulic cylinders into gripping engagement with the sides of the rail section webs and serve simultaneously as electrodes for the welding current and for clamping the rail section ends therebetween. Flash-butt welding is effected by operating hydraulic cylinders connected to the welding heads to press the welding heads and the rail section ends gripped thereby towards each other at a speed of about 0.25 mm per second and conducting electric current through the electrodes. When the rail section ends come into contact with each other, the electric current reaches a first peak value and the movement of the welding heads towards each other is stopped to obtain a suitable melting temperature. The flash-butt welding operation is concluded by a compression stroke which causes the abutting rail section ends heated to the melting temperature to be pressed against each other under very high compression forces. To facilitate the compression stroke, particularly in the case of very long and heavy rail sections, the welding heads are surrounded by a ring-shaped rail tensioning mechanism. This mechanism comprises pivotal tongs with clamping jaws for grippingly engaging the sides of the webs of both rail sections. The compression stroke is effected by the synchronous operation of the cylinders pressing the welding heads towards each other and cylinder pivoting the tongs into gripping engagement with the web sides of the rail sections.
German patent No. 1,465,042, published July 31, 1969, also discloses a flash-butt welding unit for welding together adjacent ends of track rail sections. This unit comprises two welding heads longitudinally displaceable towards each other by cylinders extending in a longitudinal direction, each welding head comprising two parts pivotal towards each other about a longitudinally extending axis. Clamping electrodes are mounted on lower ends of the welding head parts for engaging the sides of the rail section ends, and a cylinder connects the upper ends of the welding head parts for pivoting the same into engagement with the rail section end sides.
Swiss patent No. 632,948, dated Nov. 15, 1982, discloses a stationary welding unit with a complex mechanism for centering adjacent profiled rod ends to be welded together. To provide the required welding pressure, a clamping device is longitudinally displaceable by means of pressure cylinders which are connected to a fixed support. This differs fundamentally from the welding unit of this invention, which comprises two longitudinally displaceable welding heads pressed against each other by actuating cylinders, which arrangement makes the complicated centering mechanism of this patent unnecessary.
British patent application No. 2,104,818, published Mar. 16, 1983, discloses a mobile welding unit including a fixed assembly and an assembly movable towards the fixed assembly. Each assembly has two clamping devices for aligning the adjacent rail section ends during welding.